The present invention is directed to bone anchoring and more particularly to an anchoring method and system for reducing the potential for an anchor to pull out of bone.
Various bone anchors have been developed for mounting structures to bones. For example, rods and/or plates are often attached to vertebrae using anchors such as screws or hooks. In the past, most procedures of this type rigidly held the separate bone elements in fixed positions relative to one another so that over time the bone elements would grow together or fuse. In some instances, metal cables and/or wires were looped around portions of vertebrae and the rods or plates extending between the anchors to securely hold the vertebrae in their respective positions to promote healing and/or fusion.
Sometimes bone is weak and brittle making it difficult to fasten the anchors to the bones. One such example of weak and brittle bones is in patients having osteoporosis. In such instances, screws and hooks may not offer reliable fastening and are prone to failure prior to solid fusion. Further, some surgical techniques do not rigidly fix the bone elements, but allow the bone elements to move a limited distance. This movement can change the loading on the anchors and cause the anchors to pull out of the bone over time. Thus, there is a need for an anchoring system having improved anchoring characteristics and resists pulling out under one or more of these conditions.